Among the commands of a machine, probably, the emergency stop is the most visible one; however it is not the easiest to understand.
The reference standard is the ISO 13850, whose latest edition was published in November 2015: "Safety of machinery - Emergency Stop Function – Principles for design".
The definition is (§3.1): ”function which is intended to avert arising or reduce existing hazard to person, damage to machinery or to work in progress; and be initiated by a single human action”.
In this article some important aspects are discussed; Please refer to the standard to understand all the requirements and for a correct implementation of the function.
Should the Reset button in a machinery be handled by a safety module, or can it be one of several inputs to the Automation PLC?
The question can be rewritten in a more correct language by asking if the Reset is a Safety Function.
Often the manufacturer has doubts about what should be indicated in the Instruction manual.
One of the aspects is whether it is necessary to report the spare parts list. What obligation does the manufacturer have in this regard?
The drawing up machinery instructions is an obligation of the manufacturer. Point 1.7.4 of the Machinery Directive 2006/42/EC deals with the obligations to be met regarding the Instructions for Use, before the machine is placed on the market and/or put into service.
RESS 220.127.116.11 details the contents of the instructions for safe use of the machine. The letter t) specifies that the User Manual must contain:
t) the specifications of the spare parts to be used, when these affect the health and safety of operators;
The following is defined in the Guideline of Directive 2006/42/EC:
“Section 18.104.22.168 (t) refers to information about spare parts. In general, the supply of spare parts and the supply of a spare parts list are not covered by the provisions of the Machinery Directive and is thus a matter for contractual agreement between the manufacturer and the user. However, where parts subject to wear and tear need to be replaced in order to protect the health and safety of users, the specifications of the appropriate spare parts must be given in the instructions.
Examples of such spare parts include:
• guards for removable mechanical transmission devices;
• flexible guards subject to wear and tear;
• comments on section;
• filters for systems to provide clean air to operating positions;
• load bearing components on lifting machinery;
• guards and their fixing systems used to retain ejected objects or parts of machinery.”
Therefore, the spare parts list is mandatory to issue the CE certification of a machine if they are parts subject to wear and that could affect the safety.
EN 60204-1 "Safety of machinery - Electrical equipment of machines Part 1: General requirements",
there are three categories of stop functions:
- Stop Category 0: stopping by immediate removal of power to the machine actuators (i.e. an uncontrolled stop);
- Stop Category 1: a controlled stop with power available to the machine actuators to achieve the stop and then removal of power when the stop is achieved;
- Stop Category 2: a controlled stop with power remaining available to the machine actuators.
These three categories are taken from specific standards such as ISO 13850 and IEC 61800-5-2.
The assessment and risk reduction process is detailed in various standards.
An important aspect of the risk reduction methods suggested by the standards concerns the reduction of energy levels.
When possible, access to a segregated area should be carried out at zero energy with the elimination and isolation of hazardous energy (preferred method to reduce the risk). However, some activities require partial or total energization to be performed and to operate machine elements with disabled protection devices. For these specific activities, reduced energy operating modes are are a way to reduce the risk for the operator or the maintenance person.
Some types of machines are subject to specific standards that define the operating modes in terms of reduced energy values and other additional conditions.
However, many others, are not covered by a specific standard and therefore manufacturers may not know what threshold to use.
Here we present some values stated in technical standards, grouped in the following way:
- Speed (mm / s): to be used in case of objects that move at constant speed (Robot arm).
- Force (N): in case of constant pressure without acceleration of the element.
- Kinetic Energy (J): to be used in case of objects that move at increased speed (a gate/protection falling from a certain hight).
- Pressure (N / cm2). In case certain part of the body is subject to the possible damage.